Semiconductor manufacturing has historically used 18 MOhm/cm deionized water as a rinsing and cleaning fluid. Semiconductor manufacturers put water through a sequence of steps to remove particles and metal ions that would otherwise poison semiconductor devices. Once these impurities are removed from water the resistivity is typically raised to 18 MOhm/cm. DI water in many cases is used as a pressurized medium to remove particles from the surfaces of wafers. These particles would otherwise cause defects in the semiconductor devices on the wafers. The undesired side effect of pressurized dispense of deionized water on wafers is the build of static voltages and eventually electrostatic discharge (ESD). Many semiconductor devices are ESD sensitive and if voltages are permitted to build and then discharge, yield loss will occur.
The static voltages are created when a non conductive fluid (such as 18 MOhm/cm DI) aggressively contacts a non-conductive (or electrically isolated) surface (such as a wafer). The voltage built will be proportional to the aggressiveness (force) of the dispense and proportional to the resistivity of the fluid employed. The cleaning efficiency of the water dispense is also proportional to the force of the spray. This leads to the paradox of high pressure spray being required to remove particles from the wafer surface to increase yield, but high pressure spray causing static voltage to build to the point of discharge causing yield loss.
The industry has used carbon dioxide to lower the resistivity of the DI water. Systems currently used metal components such as 316SS (stainless steel) tanks, piping and fittings in the DI water:CO2 mixing system. These systems were successful at reducing the resistivity levels of the DI water but the metal components in the plumbing path added metal ions into the DI water. These metal ions could re-deposit on semiconductor devices and interfere with their operation.
There is therefore a need to provide a solution to this problem.